Field of Invention
The present invention relates to a front light module and an electronic paper display device.
Description of Related Art
In the market full of a wide variety of consumer electronic products, portable electronic devices, e.g. an electronic book, now have extensively utilized electronic paper display devices as display screens. A display medium layer (also referred to as an electronic ink) of an electronic paper display device is mainly made of an electrophoresis buffer and white and black charged particles doped in the electrophoresis buffer. The white and black charged particles are movable driven by applying a voltage to the display medium layer, so as to present individual pixel with black, white or a gray level.
In the present technology, the electronic paper display device utilizes an incident light that irradiates the display medium layer to achieve the purpose of display. Therefore, the electronic paper display device needs no backlight, which reduces the power consumption of the electronic paper display device. In order to expand the application of the electronic paper display device, a front light module is often arranged above the front panel laminate of the electronic paper display device. Even if the electronic paper display device is used in a place with insufficient ambient light, the front light module may emit an incident light to the display medium layer. As such, users can see the images displayed by the electronic paper display device.
The conventional front light module of the electronic paper display device may consist of a light source, a light guide plate, and a light transmissive protection cover having an ink layer printed thereon. The surface of the light transmissive protection cover having the ink layer is adhered to the light guide plate. The ink layer is printed on the edge of the light transmissive protection cover to be a frame for shielding light. However, the light emitted by the light source is guided to the external surface of the light transmissive protection cover. The perpendicular distance between the external surface of the light transmissive protection cover and the ink layer is so far that the light is apt to be reflected to the ink layer by the external surface of the light transmissive protection cover, resulting in and the fluorescent illumination and visual interference. In this regard, only a dark (e.g., black) ink layer is optional to reduce the influence of the fluorescent illumination. The limitation in choosing the colors of the ink layer restricts the change in the color of the housing of the electronic paper display device. On the other hand, an additional air gap may be used to change the refraction direction of the light, which however scarifies the transmittance of the front light module.